The present disclosure relates generally to metal plating, particularly to tin platings.
The transition to lead-free electronics is resulting in suppliers of electronic components converting product lines from tin/lead to lead-free finishes. The suppliers often use pure electroplated tin as a lead-free finish. However, pure tin platings have a propensity to form tin whiskers. For example, tin whiskers have been found to form on a wide variety of tin-plated component types under a range of environmental conditions. These whiskers are comprised of nearly pure tin and are therefore electrically conductive and can cause shorting of electronics. The growth of whiskers has caused, and continues to cause, reliability problems for electronic systems that employ components that are plated with tin, which includes, for example, manufacturers of high-reliability systems and government users. Moreover, field failures attributable to tin whiskers can cost millions of dollars and result in customer dissatisfaction.
The factors that cause tin whiskers to grow are not well understood, although stress in the plating is believed to be a key factor. The effects of plating process parameters such as current density, temperature, substrate preparation, substrate material, and bath components have been studied. In addition, the effects of plating thickness, underlayers, post-plating annealing, plating structure, and alloying agents on whisker growth have been explored. The crystallographic structure of tin whiskers has also been studied.
Thus, with respect to the issue of tin whisker growth, while it would be desirable to remove pure tin from an electronic system, increasing use of tin by electronic component vendors and the increasing use of COTS (commercial-off-the-shelf) components in high-reliability systems makes such removal difficult to implement.
Another approach includes dipping all tin-plated component leads into molten tin/lead (up to the component body). However, this can damage the component package which allows intrusion of moisture into the package. In addition, the dipping operation is expensive.
Thus, known methods for controlling tin whisker growth can be difficult to implement and/or can result in adverse effects.